The Mercedes-Benz W116 is a series of flagship luxury sedans produced from September 1972[2] until 1980.[3] The W116 automobiles were the first Mercedes-Benz models to be officially called S-Class, although earlier sedan models had already unofficially been designated with the letter 'S' – for Sonderklasse or "special class."

The 'new' S-class generation development began in 1966, which was only a year after the launch of the W108/09. This was the first Mercedes saloon to feature the brand new corporate styling theme which was to be continued until 1993 when the 190 was discontinued. The design, finalized in December 1969[4] was a dramatic leap forward, with more masculine lines that combined to create an elegant and sporty character. The basic design concept carried through the themes originally introduced on the R107SL-Classroadster, especially the front and rear lights.[1] As for the SL, the W116 received the ridged lamp covers which kept dirt accumulation at bay; this was to remain a Mercedes-Benz design theme into the 21st century.[5] The W116 was Friedrich Geiger's last design for Mercedes-Benz; his career had started with the Mercedes-Benz 500K in 1933.

The car was presented in September 1972. The model range initially included two versions of the M110 engine (Straight-six with 2746 cc displacement)—the 280 S (using a Solex carburetor) and the 280 SE (using Bosch D-Jetronic injection), plus the 350 SE, powered by the M116 engine (V8 with 3499 cc displacement). After the 1973 Fuel Crisis, a long-wheelbase version of the 280 was added to the lineup.

Half a year later, in early 1973, two new models powered by the M117 engine (V8 with 4520 cc displacement) were added to the range—the 450 SE and the 450 SEL (with a 100 mm longer body). The 450 had 225 PS (165 kW) in most markets, federalized cars offered 190 hp (142 kW) while Swedish market cars had an EGR-valve and 200 PS (147 kW) until 1976.[5] The 450s received a plusher interior as well, with velour or leather seats rather than the checkered cloth of the lesser models. The door insides were also of a different design, being pulled up around the windows.[6]

The most notable W116 was the high-performance, limited-production 450 SEL 6.9, which was introduced in 1975. This model boasted by far the largest engine installed in a post-war Mercedes-Benz (and any non-American production automobile) up to that time,[7] and also featured self-levelinghydropneumatic suspension.

The 300 SD sedan (American market only) had a turbocharged 3.0-litre inline-fivediesel engine developed from the C111 experimental vehicle. In September 2013, a 1979 W116 300 SD was campaigned in the 24 Hours of Lemons at Carolina Motorsports Park, where it completed 166 laps at an average speed of 54.8 MPH.[8] It won the highest prize of the event, the Index of Effluency. Other than mild issues relating to brake and tire wear, no mechanical issues were encountered. After numerous modifications to handling, the car was again run in February 2014 at Barber Motorsports park in Birmingham, AL. It placed 44th, but turned 281 laps at an average pace of 59.6 MPH. One of the key advantages of the 300 SD is its exceptional fuel economy on track, where it burns just 2.5 GPH (Roughly 18MPG). In July 2014 it placed first in class at Sebring. It is still active in the series.[9]

In 1975, the W116 was upgraded with a new fuel injection system to comply with revised exhaust emission standards in European markets. A slight power reduction was a result of this update. In 1978, a series of engine upgrades restored original performance levels with new fuel injection systems. Initially the early models (1973-1974) of the W116 with the Twin Cam inline 6 used the D-Jetronic fuels injection system with computers and MAP sensor that are both prone to failure after more than 20 years of use. From 1975 onward they used the K-Jetronic mechanical fuel injection system, a less complicated system that proved to be much more reliable in the long run and injectors cost 6x less than the D-jetronic system. The W116 equipped with the K-Jetronic system, used a cast-iron fuel distributor, which can be prone to rust over time if moisture or water is present in the fuel. This was changed to an alloy fuel distributor in the following model W126 and is not subject to corrosion.

The high-performance 450 SEL 6.9 version of the S-Class was built on its own assembly line by Daimler-Benz in Stuttgart, Germany and based on the long-wheelbase version of the W116 chassis. The model was generally referred to in the company's literature as the "6.9", to separate it from the regular 450 SEL.

The 6.9 was first shown to the motoring press at the GenevaAuto Show in 1974, and produced between 1975 and 1981 in extremely limited numbers. It was billed as the flagship of the Mercedes-Benz car line, and the successor to Mercedes-Benz's original high-performance sedan, the 300 SEL 6.3. The 6.9's successor—the top of range 500 SEL—continued the 6.9's remarkable self-levelinghydropneumatic suspension as an extra-cost option.

The 6.9 was the first Mercedes-Benz to be fitted with the hydropneumaticself-levelling suspension system introduced by Citroën in 1954, unlike the 600 and 6.3 which employed air suspensions. Using a combination of fluid-filled struts and nitrogen-filled pressure vessels or "accumulators" in lieu of conventional shock absorbers and springs, the system was pressurized by a hydraulic pump driven by the engine's timing chain. Compared to the new Mercedes-Benz system, Citroën's was belt-driven, exactly like a conventional power steering pump; failure of the Citroën system thus might result in loss of suspension. Conversely, every unit of the 6.9 was shipped with hard rubber emergency dampers that served as temporary springs and allowed the car to be driven in the event of a hydraulic failure. The special hydraulic fluid required by the system was stored in a tank inside the engine compartment. Not only was the system totally self-adjusting, ride height could be altered by a dash-mounted push-pull knob under the speedometer that raised the car an additional two inches (50 mm) for increased ground clearance.

Four-wheel disc brakes and four-wheel independent suspension were standard on these top-of-the-line models. The M100 engine is a cast ironV8 with single overhead camshafts which was a bigger version of the engine also used in the Mercedes-Benz 600 and the Mercedes-Benz 300SEL 6.3. Notable is the Bosch K-Jetronic electromechanical fuel injection, forged crankshaft, connecting rods and pistons, and a "dry sump" engine lubrication system. As a result, the engine itself had no dipstick for checking the oil level. Rather, the dipstick was attached to the inside of the tank's filler cap (accessible from the engine compartment) and the oil level was checked with the engine running and at operating temperature. The non-American market trim version of the 6.9 l (6,834 cc or 417 in³) power plant was rated at 286 PS (210 kW) and 405 lb·ft (549 N·m) of torque, helping to compensate for the 2.65 to 1 final drive ratio necessary for sustained high-speed cruising. The dry sump system also had the benefit of extending the oil change interval to 12,500 miles (20,000 km). This, along with hydraulic valve lifters which required no adjusting and special cylinder head gaskets which eliminated the need for periodic retorquing of the head bolts, made the 6.9 relatively easy to maintain and service for its first 50,000 miles (80,500 km). The 6.9 required little basic service other than coolant, minor tune-ups, oil changes, and replacement of the air, fuel, oil and power steering filters.

Top speed was factory-rated at 140 mph (225 km/h), but some journalists testing the car saw speeds approaching 150 mph (241 km/h). Among those journalists was Brock Yates. Yates was approached by the factory to write promotional literature about the 6.9 for advertising purposes. He agreed under the condition that he could list the car's faults as well as its positives and create a genuine extensive review. Daimler-Benz agreed in turn, and Yates was given an American-market spec 6.9 to drive from Manhattan to the Road Atlanta grand prix race track in Georgia. There, Yates would drive the car in as-arrived condition at racing speeds for a full 40 laps or just over 100 miles (160 km). His complaint on this long drive on public roads was that the magnetic CB antenna blew off at 130 miles per hour. The only change made to the car upon its arrival at Road Atlanta was an adjustment of tire pressure. Driving 40 laps was a difficult task for the street-legal full size luxury sedan primarily designed and geared for comfortable Autobahn cruising. The 6.9 suffered no major mechanical problems and averaged a respectable 72 mph (116 km/h) throughout the test, completing it with little more than excess dust on the bodywork from the Michelinradial street tires on which the car was driven to Atlanta. Yates was so comfortable driving the 6.9 around the track that he reported having run at least one lap with the sunroof open and the radio on, but the high price of the car made him think better of such risky driving and he finished the test with the radio off and both hands on the wheel.[12]

All of this technology came at a very high price. At a time when the most expensive Cadillacs, the mid-sized Seville and full-sizedCadillac FleetwoodSeries Seventy-Fivelimousine each listed for about US$16,000, the 6.9 listed for around $40,000, more than the Big Three but less than most Rolls-Royces. When the car was officially introduced into the North American market for the 1977 model year, the price was well past $40,000 and was $52,995 by the end of production. Though the 6.9 was undeniably a luxury car, the decor was rather austere compared to the sheer opulence available in a Rolls-Royce or full-sized Cadillac. The interior was identical to that in the less expensive models except for the push-pull suspension control knob just under the speedometer, a low suspension pressure warning and height adjustment indicator lights in the instrument cluster, and wood trim finished in burled walnut veneer on the dash and console. The rest of the W116 lineup was trimmed in striated zebrano veneer.

The 6.9 lacked expected luxury touches such as power-adjustable outside mirrors or front seats, although a unique power rear seat, heated seats and even orthopedically designed front seats were options. Buyers outside North America could also opt for headlight wipers and washers and/or headlights with a special vacuum-operated linkage whose aim could be adjusted at the dash depending on vehicle load. There was also a new standard feature in 1976: most Mercedes-Benz automobiles that year were equipped with a sophisticated electronic climate control system developed for Chrysler Corporation for use in their top models. The system turned on the heater, air conditioner or both, depending on the thermostat's setting and ambient temperature, automatically maintaining whatever temperature the driver selected. The compressor was an American import as well, supplied by the Harrison division of General Motors.

Far more modern than the contemporary Cadillac, which still had a live rear axle, and both faster and larger inside than the either the Rolls-Royce or Cadillac, the 6.9 was indistinguishable from its W116 stablemates save for a modest "6.9" badge on the decklid and wider tires.[13] US models also had different bumper rubbers fitted to the more protruding "park bench" impact absorbing bumpers. As discreet as the badge was, it could be deleted/ordered with option 261 omission of the displacement figure on the trunk lid at extra cost for those who wanted to avoid attention either from drivers of other high-performance cars or from law enforcement. In the words of David E. Davis, the 6.9 was "a $50,000 exercise in going fast."

Still, for fans of the discontinued 6.3 or for those who simply had to have a car which Car and Driver proclaimed to be "the greatest Mercedes-Benz ever built," it seemed that money was no object. At its launch in 1975, the 450 SEL 6.9 cost DM 69,930. In the last year of production, 1979, the car was available at a price of DM 81,247. Even though this was far from inexpensive, the courage of the Mercedes-Benz strategists in launching the car onto the market paid off. A total of 7,380 units were built by 1980, and most of these were exported to the USA. This volume is quite respectable considering the overall sales trend of powerful luxury cars following the 1973 energy crisis.

In a poll conducted by Britain's Classic & Sports Car magazine and printed in their April 1999 edition, the Mercedes-Benz 6.9 ranked fourth on their list of the "world's greatest saloons."[14] The May 2004 edition of another British publication, Mercedes Enthusiast magazine, ranked the 6.9 number fifteen on their all-time top twenty list of great Mercedes-Benz automobiles. Even with such accolades, a 6.9 is a reasonably priced collectible automobile despite its rarity. The online NADA Used Car Guide lists a top value of US$40,000. At present, the market for cars of this type is somewhat soft, and a prime example can be had for considerably less. As is often the case with older cars that contain exotic engineering and parts unique to that one model, however, running and maintenance costs for a 6.9 can quickly overshadow a low initial purchase price.

Four wheel anti-lock brakes were first featured as an option on the 1978 W116 S-Class. This system prevents the wheels from locking while braking. The system improves steering control during hard braking situations, and to shorten brake distances.

Strengthened body structure. The W116 featured a more stable security passenger cell with a stiffened roof frame structure. High strength roof and door pillars, along with other reinforced zones, provided enhanced vehicle occupant protection.

Deformation zones (crumple zones) in the front and rear.

A padded dashboard, deformable switches and controls, and a four-spoke steering wheel with impact absorber and broad impact cushion aimed to reduce occupant injury during collisions.

The fuel tank was no longer fitted at the rear end, but was now placed above the rear axle for added protection.

Wraparound turn signals made it easier to communicate with nearby drivers.

International M-100 Group — Factory-authorized site with information on all M-100-powered Mercedes-Benz automobiles, (including technical forums and maintenance information). The Brock Yates article can be found here as well